The present invention relates generally to an indexing device, for use in a centrifuge device, which rotates a blood tube about its longitudinal axis while the blood tube is being rotated by the centrifuge device. More particularly, the present invention relates to an indexing device which is coupled to the rotor of a centrifuge device, and which is controlled by relative movement of the rotor to rotate a blood tube in the rotor about an axis substantially corresponding to the longitudinal axis of the blood tube, while the rotor is spinning the blood tube, so that images of the centrifuged blood can be obtained from different locations about the circumference of the blood tube.
As part of a routine physical or diagnostic examination of a patient, it is common for a physician to order a complete blood count for the patient. The patient's blood sample may be collected in one of two ways. In the venous method, a syringe is used to collect a sample of the patient's blood in a test tube containing an anticoagulation agent. A portion of the sample is later transferred to a narrow glass capillary tube, known as a sample tube. The open end of the sample tube is placed in the blood sample in the test tube, and a quantity of blood enters the sample tube by capillary action. In the capillary method, the syringe and test tube are not used and the patient's blood is introduced directly into sample tube from a small incision made in the skin. In either case, the sample tube is then placed in a centrifuge, such as the Model 424740 centrifuge manufactured by Becton Dickinson and Company.
In the centrifuge, the sample tube containing the blood sample is rotated at a desired speed (typically 8,000 to 12,000 rpm) for several minutes. The high speed centrifugation separates the components of the blood by density. Specifically, the blood sample is divided into a layer of red blood cells, a buffy coat region consisting of layers of granulocytes, mixed lymphocytes and monocytes, and platelets, and a plasma layer. The length of each layer can then be optically measured, either manually or automatically, to obtain a count for each blood component in the blood sample. This is possible because the inner diameter of the sample tube and the packing density of each blood component are known, and hence the volume occupied by each layer and the number of cells contained within it can be calculated based on the measured length of the layer. Exemplary measuring devices that can be used for this purpose include those described in U.S. Pat. Nos. 4,156,570 and 4,558,947, both to Stephen C. Wardlaw, and the QBC.RTM. "AUTOREAD" hematology system manufactured by Becton Dickinson and Company.
Several techniques have been developed for increasing the accuracy with which the various layer thickness in the centrifuged blood sample can be determined. For example, because the buffy coat region is typically small in comparison to the red blood cell and plasma regions, it is desirable to expand the length of the buffy coat region so that more accurate measurements of the layers in that region can be made. As described in U.S. Pat. Nos. 4,027,660, 4,077,396, 4,082,085 and 4,567,754, all to Stephen C. Wardlaw et al., and in U.S. Pat. No. 4,823,624, to Rodolfo R. Rodriguez et al., this can be achieved by inserting a precision-molded plastic float into the blood sample in the sample tube prior to centrifugation. The float has approximately the same density as the cells in the buffy coat region, and thus becomes suspended in that region after centrifugation. Since the outer diameter of the float is only slightly less than the inner diameter of the sample tube (typically by about 80 .mu.m), the length of the buffy coat region will expand to make up for the significant reduction in the effective diameter of the tube that the buffy coat region can occupy due to the presence of the float. By this method, an expansion of the length of the buffy coat region by a factor between 4 and 20 can be obtained. The cell counts calculated for the components of the buffy coat region will take into account the expansion factor attributable to the float.
Another technique that is used to enhance the accuracy of the layer thickness measurements is the introduction of fluorescent dyes (in the form of dried coatings) into the sample tube. When the blood sample is added to the sample tube, these dyes dissolve into the sample and cause the various blood cell layers to fluoresce at different optical wavelengths when they are excited by a suitable light source. As a result, the boundaries between the layers can be discerned more easily when the layer thickness are measured following centrifugation.
Typically, the centrifugation step and the layer thickness measurement step are carried out at different times and in different devices. That is, the centrifugation operation is first carried out to completion in a centrifuge, and the sample tube is then removed from the centrifuge and placed in a separate reading device so that the blood cell layer thicknesses can be measured. This added step of removing the blood tube from the centrifuge device increases the time needed to complete the layer reading process. Furthermore, because the tubes must be handled and moved between the centrifuging device and layer reading device, the likelihood that damage to the tubes can occur is increased. Additionally, because the centrifuging is stopped when the blood tube is being moved from the centrifuge device to the layer reading device, the blood components that have been compacted into their individual layers due to the centrifugation may begin to migrate into adjacent layers, thus resulting in inaccurate readings. Also, since the centrifuge can "spin down" multiple sample tubes, the manual transfer to the reading devices increases the chance of sample ID error.
More recently, a technique has been developed in which the layer thicknesses are calculated using a dynamic or predictive method while centrifugation is taking place. This is advantageous not only in reducing the total amount of time required for a complete blood count to be obtained, but also in allowing the entire procedure to be carried out in a single device. Apparatus and methods for implementing this technique are disclosed in the aforementioned copending applications of Stephen C. Wardlaw entitled "Assembly for Rapid Measurement of Cell Layers", Ser. No. 08/814,536, now U.S. Pat. No. 5,889,584 and "Method for Rapid Measurement of Cell Layers", Ser. No. 08/814,535 now U.S. Pat. No. 5,888,184.
In order to allow the centrifugation and layer thickness measurement steps to be carried out simultaneously, it is necessary to "freeze" the image of the sample tube as it rotates at high speed on the centrifuge rotor. This can be accomplished by means of a xenon flash lamp assembly that produces an intense excitation pulse of light energy once per revolution of the centrifuge rotor. The pulse of light excites the dyes in the expanded buffy coat area of the sample tube, causing the dyes to fluoresce with light of known wavelengths. The emitted fluorescent light resulting from the excitation flash is focused by a high-resolution lens onto a linear array of charge-coupled devices (CCDs). The CCD array is located behind a bandpass filter which selects the specific wavelength of emitted light to be imaged onto the CCD array.
The xenon flash lamp assembly is one of two sources that are used to illuminate the sample tube while the centrifuge rotor is in motion. The other source is an array of light-emitting diodes (LEDs) which transmit red light through the sample tube for detection by the CCD array through a second bandpass filter. The purpose of the transmitted light is to locate the beginning and end of the plastic float (and hence the location of the expanded buffy coat area), and the fill lines. Further details of the optical reading apparatus may be found in the aforementioned copending application of Bradley S. Thomas et al. entitled "Blood Centrifuge Device with Movable Optical Reader", Ser. No. 09/033,368.
In order to obtain an accurate measurement of the lengths of the blood component layers, it is necessary to take a sample of readings about the circumference of the tube. That is, when the blood is centrifuged so that layers of the blood components are formed in the tube, it is likely that the lengths of the layers will not be uniform across the entire inner diameter of the tube. Rather, it is common for a layer to have a longer length on one side of the tube and a shorter length on the other side. Because the cell count calculations are based on the measured length of the layers, if the measurements are taken from only one side of the tube, it is likely that inaccurate cell counts will be calculated.
Accordingly, it is desirable to rotate the tube of centrifuged blood so that readings can be taken at various locations (e.g., 8 different locations) about the circumference of the tube. The respective readings for each layer are then averaged, so that an average length is computed for each layer. The average length for each layer is used to calculate the cell count for each respective blood component in the centrifuged blood sample, thus providing more accurate cell counts.
One method for rotating the tube of centrifuged blood about its longitudinal axis while the sample tube remains in the centrifuge device and is being spun by the rotor of the centrifuge device is disclosed in a copending U.S. patent application of Michael R. Walters entitled "Centrifugally Actuated Tube Rotator Mechanism" (Ser. No. 08/918,437), now abandoned. This apparatus includes a cylindrical cup that receives one end of the sample tube, and a cam mechanism that operates to operate the cup about its longitudinal axis. The cam mechanism is driven by changing the speed of the rotor. That is, as the speed of the rotor is changed, the cam mechanism is driven radially of the rotor, and translates this radial movement into rotational movement which rotates the cup and the tube received therein.
Although the apparatus described in the copending U.S. patent application of Michael R. Walters et al. entitled "Centrifugally Actuated Tube Rotator Mechanism" (Ser. No. 08/918,437), now abandoned is effective for its intended purpose, a continuing need exists for an apparatus which is capable of centrifuging a blood sample stored in a capillary tube and taking accurate measurements of the component layers of the centrifuged blood sample while allowing the capillary tube to remain in the centrifuge device. The present invention is directed to that objective.